期刊
CATALYSIS LETTERS
卷 146, 期 9, 页码 1749-1770出版社
SPRINGER
DOI: 10.1007/s10562-016-1800-z
关键词
FeNC; ORR; Oxygen reduction reaction; Mossbauer spectroscopy; Planar FeN4
资金
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-FG02-07ER15896]
- Ohio Coal Research Consortium [OCRC-C-04]
- E.I. DuPont de Nemours Co.
- Dow Chemical Company
- Northwestern University
- U.S. DOE [DE-AC02-06CH11357]
The objective of this study was to understand the role of iron and the heat treatment steps involved in nitrogen-coordinated iron-carbon (FeNC) catalyst synthesis. We have studied the oxygen reduction reaction (ORR) performance of these catalysts as they evolve from their most crude and inactive form to their most active form. Electrochemical half-cell and fuel cell tests suggest that the presence of Fe was crucial in these samples. The high-temperature heat treatment (once in argon and then in ammonia) at temperatures aeyen950 A degrees C were also critical in imparting these catalysts with their highest activity; however, significant loss of activity was observed with cycling and potential hold at 0.5 V for 100 h. In addition, acid-washing after the first or the second pyrolysis steps produced a marked decrease in ORR activity relative to their unwashed counterparts. We also report findings from our efforts towards benchmarking FeNC catalysts for oxygen reduction reaction electrocatalysis. Specifically, we focus on correlating the specific kinetic current (i(K)) at 0.75 V to electrochemically accessible surface area (EASA) and roughness factor (RF) determined from electrochemical double layer capacitance measurements. Fe-57 Mossbauer spectroscopy was employed to shed light into the nature of active sites in FeNC catalysts and provide insights into their deactivation behavior caused by acid-washing. The results suggest planar FeN4 doublet (Fe2+, low spin) as an active site in these materials, which may be leached away in acid, explaining their decreased activity after acid washing. Results for characterization experiments using X-ray photoelectron spectroscopy, temperature programmed oxidation and X-ray absorption spectroscopy, superconducting quantum interference device magnetometry are also presented.
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